1. Field of the Invention
The present invention relates to the field of manufacturing bags in a xe2x80x9cstringxe2x80x9d, i.e. bags that are connected one after another on leaving the manufacturing process, but suitable for being separated during a subsequent filling step or after filling.
The present invention relates more precisely to manufacturing bags provided with complementary closure strips suitable for enabling the bags to be opened and closed in alternation, on demand.
2. Description of the Related Art
Various processes have already been proposed for this purpose.
In general, systems presently known and used for making strings of bags are adapted to make strings in which the bags possess longitudinal openings, i.e. openings situated along one of the longitudinal edges of the string. Examples of such known means for making such strings are to be found in documents WO-A-94/19250 and EP-A-0 054 564.
The strings of bags obtained in that way have already given good service. Nevertheless, they do not always give satisfaction. In particular, such strings of bags with longitudinal openings require the string to be rolled out in a generally horizontal direction, if the bags are to be filled merely under gravity. Such a configuration requires an installation that is bulky. It also requires complex means for guiding the bags.
Attempts have indeed been made to avoid those difficulties by proposing means designed to make strings of bags that have transverse openings. Nevertheless, present attempts on those lines have not given complete satisfaction either.
Thus, document U.S. Pat. No. 5,118,202 proposes means for manufacturing a string of bags, adapted to place the closure strips longitudinally, while simultaneously making transverse openings on the strings. Those installations have complex means for making the transverse openings, and above all they require a bonding operation to close the bags after they have been filled, since the closure strips cannot be used for that purpose given that the closure strips extend longitudinally and not transversely like the openings.
Document WO-A-97/06062 describes other means for manufacturing a string of bags with transverse openings, adapted to place the closure strips transversely. However, in that case also the implementation means are complex. In particular they require a closure system having two complementary male/female strips whose support webs are fixed on a common sheet of the bag.
Document DE-A-3 824 753 describes a method of manufacturing a string of bags and the string of bags obtained thereby, using film that is fed onto a filling chute and that is provided with transverse complementary closure strips.
An object of the present invention is to propose novel means designed to make a string of bags.
According to the present invention, this object is achieved by a method comprising the steps which consist in sequentially placing closure system segments transversely on at least one film for forming the walls of the bag, each segment comprising two complementary closure strips, in fixing the support webs of the two complementary closure strips respectively to the inside faces of the two walls of the bag, and in providing sequential transverse openings through part of the film so as to give access to between the two strips from the outside of the closure system relative to each bag.
In a preferred implementation, the method of the present invention consists in placing transversely on the film closure system segments of a length that is about half the width of said film, in cutting the film transversely over substantially half its width outside the closure system, in folding the film over onto itself, and in fixing the support webs of the two strips of the closure system to the two walls of the bag, respectively.
The present invention also provides a machine for implementing the above method, and strings of bags obtained thereby.
The machine comprises means for sequentially placing closure system segments transversely on at least one film for forming the walls of the bag, each segment comprising two complementary closure strips, means for fixing the support webs of the two complementary closure strips respectively to the inside faces of the two walls of the bag, and the machine is characterized by the fact that it comprises means for providing sequential transverse openings through part of the film so as to give access to between the two strips from the outside of the closure system relative to each bag.
Still more precisely, the machine of the present invention preferably comprises means for placing transversely on the film closure system segments of a length that is about half the width of said film, cutting the film transversely over substantially half its width outside the closure system, folding the film over onto itself, and fixing the support webs of the two strips of the closure system to the two walls of the bag, respectively.
Strings of bags of the present invention have closure system segments comprising pairs of complementary closure strips with support webs that are fixed transversely respectively to the inside faces of the walls of the bags, the strings being characterized by a transverse opening provided through part of the film to provide access to between the two strips from the outside of the closure system relative to each bag.